Display device

ABSTRACT

A display device includes a first reflective electrode disposed on a surface of a substrate, a second reflective electrode spaced apart from the first reflective electrode and disposed on the surface of the substrate, and a light emitting element disposed between the first reflective electrode and the second reflective electrode. The first reflective electrode includes first surface irregularities disposed on a top surface of the first reflective electrode. The second reflective electrode includes second surface irregularities disposed on a top surface of the second reflective electrode.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and benefits of Korean PatentApplication No. 10-2020-0163839 under 35 U.S.C. § 119, filed on Nov. 30,2020 in the Korean Intellectual Property Office, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND 1. Technical Field

The disclosure relates to a display device.

2. Description of the Related Art

The importance of display devices has steadily increased with thedevelopment of multimedia technology. Various types of display devicessuch as an organic light emitting display (OLED), a liquid crystaldisplay (LCD) and the like have been developed in response to suchdevelopments.

A display device is a device for displaying an image, and includes adisplay panel, such as an organic light emitting display panel or aliquid crystal display panel. The light emitting display panel mayinclude light emitting elements, e.g., light emitting diodes (LED), andexamples of the light emitting diode include an organic light emittingdiode (OLED) using an organic material as a fluorescent material and aninorganic light emitting diode using an inorganic material as afluorescent material.

It is to be understood that this background of the technology sectionis, in part, intended to provide useful background for understanding thetechnology. However, this background of the technology section may alsoinclude ideas, concepts, or recognitions that were not part of what wasknown or appreciated by those skilled in the pertinent art prior to acorresponding effective filing date of the subject matter disclosedherein.

SUMMARY

Aspects of the disclosure provide a display device having improved lightemission efficiency.

However, aspects of the disclosure are not restricted to the one setforth herein. The above and other aspects of the disclosure will becomemore apparent to one of ordinary skill in the art to which thedisclosure pertains by referencing the detailed description of thedisclosure given below.

According to an aspect of the embodiments, a display device may include,a first reflective electrode disposed on a surface of a substrate, asecond reflective electrode spaced apart from the first reflectiveelectrode, disposed on the surface of the substrate, and a lightemitting element disposed between the first reflective electrode and thesecond reflective electrode. The first reflective electrode may includefirst surface irregularities disposed on a top surface of the firstreflective electrode. The second reflective electrode may include secondsurface irregularities disposed on a top surface of the secondreflective electrode.

In an embodiment, each of the first reflective electrode and the secondreflective electrodes may comprise silver (Ag), aluminum (Al), gold(Au), platinum (Pt), palladium (Pd), indium (In), nickel (Ni), chrome(Cr), or an alloy thereof.

In an embodiment, the display device may include a first insulatinglayer disposed on the first reflective electrode and the secondreflective electrode. The first insulating layer may expose at least apart of the first reflective electrode and at least a part of the secondreflective electrode. The light emitting element may be disposed on thefirst insulating layer.

In an embodiment, the display device may include a first contactelectrode disposed on the first reflective electrode, the first contactelectrode electrically contacting the first reflective electrode exposedby the first insulating layer and electrically contacting a first end ofthe light emitting element. The display device may also include a secondcontact electrode disposed on the second reflective electrode, thesecond contact electrode electrically contacting the second reflectiveelectrode exposed by the first insulating layer and electricallycontacting a second end of the light emitting element.

In an embodiment, the display device may include a second insulatinglayer disposed on the first contact electrode and the second contactelectrode, and covering the first contact electrode and the secondcontact electrode. A refractive index of the second insulating layer maybe different from a refractive index of the first contact electrode anddifferent from a refractive index of the second contact electrode.

In an embodiment, the refractive index of the second insulating layermay be smaller than the refractive index of the first contact electrodeand smaller than the refractive index of the second contact electrode.

In an embodiment, the display device may include a filler disposed onthe first and second contact electrodes. A refractive index of thefiller may be smaller than the refractive index of the first contactelectrode and smaller than the refractive index of the second contactelectrode.

In an embodiment, the first contact electrode may electrically connectthe light emitting element and the first reflective electrode that arespaced apart from each other. The second contact electrode mayelectrically connect the light emitting element and the secondreflective electrode that are spaced apart from each other.

In an embodiment, the first contact electrode may include third surfaceirregularities that correspond to the first surface irregularities ofthe first reflective electrode and are disposed in a region where thefirst contact electrode contacts the first reflective electrode.

In an embodiment, the first surface irregularities and the secondsurface irregularities may have a same surface roughness.

In an embodiment, the first surface irregularities and the secondsurface irregularities each may have a random shape.

In an embodiment, the first surface irregularities and the secondsurface irregularities may be patterned to have a constant size.

In an embodiment, a size of each of the first surface irregularities andthe second surface irregularities may be within a range of a wavelengthband of light emitted from the light emitting element.

In an embodiment, the display device may include a first sub-bankdisposed on the surface of the substrate and including a side surfacefacing a first end of the light emitting element. The first reflectiveelectrode may be disposed on the first sub-bank. The first surfaceirregularities may be disposed in a region overlapping at least the sidesurface of the first sub-bank.

In an embodiment, the display device may include a second sub-bankspaced apart from the first sub-bank, disposed on the surface of thesubstrate, and including a side surface facing a second end of the lightemitting element. The second reflective electrode may be disposed on thesecond sub-bank, and including the second surface irregularities in aregion overlapping at least the side surface of the second sub-bank.

According to an embodiment, a display device may include a firstelectrode disposed on a substrate, and including surface irregularitiesdisposed on a top surface of the first electrode, a second electrodespaced apart from the first electrode, disposed on the substrate, andincluding surface irregularities disposed on a top surface of the secondelectrode, a light emitting element disposed between the first electrodeand the second electrode, a first contact electrode disposed on thefirst electrode, the first contact electrode electrically connecting thefirst electrode to a first end of the light emitting element, a secondcontact electrode disposed on the second electrode, the second contactelectrode electrically connecting the second electrode to a second endof the light emitting element, and an insulating layer disposed on thefirst contact electrode and the second contact electrode, and coveringthe first contact electrode and the second contact electrode. Arefractive index of the insulating layer is different from a refractiveindex of the first contact electrode and different from a refractiveindex of the second contact electrode.

In an embodiment, the refractive index of the insulating layer may besmaller than the refractive index of the first contact electrode andsmaller than the refractive index of the second contact electrode.

In an embodiment, each of the first and second electrodes may comprisesilver, aluminum, gold, platinum, palladium, indium, nickel, chrome, oran alloy thereof.

In an embodiment, the surface irregularities of the first electrode andthe surface irregularities of the second electrode may be patterned tohave a constant size.

In an embodiment, a size of each of the surface irregularities of thefirst electrode and a size of the surface irregularities of the secondelectrode is within a range of a wavelength band of light emitted fromthe light emitting element.

In the display device according to an embodiment, the light emitted fromthe light emitting element and incident on the surfaces of the first andsecond electrodes may be diffusely reflected to randomly change thelight traveling direction by including a textured surface on thesurfaces of the first and second electrodes. By randomly changing thelight traveling direction, the formation rate of an optical waveguidethat may be formed by layers arranged in the area adjacent to the lightemitting element may be reduced, and the amount of light emitted fromthe light emitting element to the outside of the layers may beincreased, thereby improving the light emission efficiency of thedisplay device.

It should be noted that the effects of the disclosure are not limited tothose described above, and other effects of the disclosure will beapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the disclosure will becomemore apparent by describing in detail embodiments thereof with referenceto the attached drawings, in which:

FIG. 1 is a schematic plan view of a display device according to anembodiment;

FIG. 2 is a schematic plan view illustrating a pixel of a display deviceaccording to an embodiment;

FIG. 3 is a schematic cross-sectional view illustrating an example takenalong line III-III′ of FIG. 2;

FIG. 4 is a schematic diagram of a light emitting element according toan embodiment;

FIG. 5 is an enlarged schematic cross-sectional view illustrating anexample of area A of FIG. 3;

FIG. 6A is an enlarged schematic cross-sectional view illustrating pathsof light emitted from a light emitting element;

FIG. 6B is an enlarged schematic cross-sectional view of area Q of FIG.6A;

FIG. 7 is a schematic cross-sectional view illustrating an example takenalong line III-III′ of FIG. 2;

FIG. 8 is a schematic cross-sectional view illustrating an example takenalong line III-III′ of FIG. 2;

FIG. 9 is a schematic cross-sectional view illustrating an example takenalong line III-III′ of FIG. 2;

FIG. 10 is an enlarged schematic cross-sectional view illustratinganother example of area A of FIG. 3;

FIG. 11 is an enlarged schematic cross-sectional view of area B of FIG.10;

FIG. 12 is an enlarged schematic cross-sectional view illustrating anexample of area A of FIG. 3;

FIG. 13 is an enlarged schematic cross-sectional view illustrating anexample of area A of FIG. 3; and

FIG. 14 is an enlarged schematic cross-sectional view illustrating anexample of area A of FIG. 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments are shown.This disclosure may, however, be embodied in different forms and shouldnot be construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the disclosure to thoseskilled in the art.

It will also be understood that when a layer is referred to as being“on” another layer or substrate, it can be directly on the other layeror substrate, or intervening layers may also be present. The samereference numbers indicate the same components throughout thespecification.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another element. For instance, a first elementdiscussed below could be termed a second element without departing fromthe teachings of the disclosure. Similarly, the second element couldalso be termed the first element.

In the drawings, sizes, thicknesses, ratios, and dimensions of theelements may be exaggerated for ease of description and for clarity.Like numbers refer to like elements throughout.

As used herein, the singular forms, “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

In the specification and the claims, the term “and/or” is intended toinclude any combination of the terms “and” and “or” for the purpose ofits meaning and interpretation. For example, “A and/or B” may beunderstood to mean “A, B, or A and B.” The terms “and” and “or” may beused in the conjunctive or disjunctive sense and may be understood to beequivalent to “and/or.”

In the specification and the claims, the phrase “at least one of” isintended to include the meaning of “at least one selected from the groupof” for the purpose of its meaning and interpretation. For example, “atleast one of A and B” may be understood to mean “A, B, or A and B.”

The spatially relative terms “below”, “beneath”, “lower”, “above”,“upper”, or the like, may be used herein for ease of description todescribe the relations between one element or component and anotherelement or component as illustrated in the drawings. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation, in addition tothe orientation depicted in the drawings. For example, in the case wherea device illustrated in the drawing is turned over, the devicepositioned “below” or “beneath” another device may be placed “above”another device. Accordingly, the illustrative term “below” may includeboth the lower and upper positions. The device may also be oriented inother directions and thus the spatially relative terms may beinterpreted differently depending on the orientations.

The terms “overlap” or “overlapped” mean that a first object may beabove or below or to a side of a second object, and vice versa.Additionally, the term “overlap” may include layer, stack, face orfacing, extending over, covering, or partly covering or any othersuitable term as would be appreciated and understood by those ofordinary skill in the art.

The terms “face” and “facing” mean that a first element may directly orindirectly oppose a second element. In a case in which a third elementintervenes between the first and second element, the first and secondelement may be understood as being indirectly opposed to one another,although still facing each other.

When an element is described as ‘not overlapping’ or ‘to not overlap’another element, this may include that the elements are spaced apartfrom each other, offset from each other, or set aside from each other orany other suitable term as would be appreciated and understood by thoseof ordinary skill in the art.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” may mean within one or morestandard deviations, or within ±30%, 20%, 10%, 5% of the stated value.

It will be understood that when an element (or a region, a layer, aportion, or the like) is referred to as “being on”, “connected to” or“coupled to” another element in the specification, it can be directlydisposed on, connected, or coupled to another element mentioned above,or intervening elements may be disposed therebetween.

It will be understood that the terms “connected to” or “coupled to” mayinclude a physical or electrical connection or coupling.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the disclosure pertains. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, embodiments will be described with reference to theaccompanying drawings.

FIG. 1 is a schematic plan view of a display device according to anembodiment.

Referring to FIG. 1, a display device 10 displays a moving image or astill image. The display device 10 may refer to any electronic deviceproviding a display screen. Examples of the display device 10 mayinclude a television, a laptop computer, a monitor, a billboard, anInternet-of-Things device, a mobile phone, a smartphone, a tabletpersonal computer (PC), an electronic watch, a smart watch, a watchphone, a head-mounted display, a mobile communication terminal, anelectronic notebook, an electronic book, a portable multimedia player(PMP), a navigation device, a game machine, a digital camera, acamcorder and the like, which may provide a display screen.

The display device 10 may include a display panel which provides adisplay screen. Examples of the display panel may include inorganiclight emitting diode display panels, organic light emitting displaypanels, quantum dot light emitting display panels, plasma display panelsand field emission display panels. In the following description, theembodiments include an inorganic light emitting diode display panel, butthe disclosure is not limited thereto, and other display panels may beapplied within the same scope of the technical spirit.

Hereinafter, a first direction DR1, a second direction DR2, and a thirddirection DR3 may be defined in drawings of an embodiment describing thedisplay device 10. The first direction DR1 and the second direction DR2may be directions perpendicular to each other in a plane. The thirddirection DR3 may be a direction perpendicular to a plane defined byfirst direction DR1 and the second direction DR2. The third directionDR3 may be perpendicular to each of the first direction DR1 and thesecond direction DR2. In an embodiment describing the display device 10,the third direction DR3 indicates a thickness direction (or displaydirection) of the display device 10.

The display device 10 may have a rectangular shape including long andshort sides such that the side in the first direction DR1 is longer thanthe side in the second direction DR2 in plan view. A corner portionwhere the long side and the short side of the display device 10 meet maybe right-angled in plan view. However, the disclosure is not limitedthereto, and it may be rounded to have a curved shape. The shape of thedisplay device 10 is not limited to the shape illustrated and may bevariously modified. For example, the display device 10 may have othershapes such as a square shape, a quadrilateral shape with roundedcorners (vertices), other polygonal shapes and a circular shape in planview.

A display surface of the display device 10 may be disposed on a side ofthe third direction DR3 which is the thickness direction. In embodimentsdescribing the display device 10, unless otherwise noted, the term“upward” refers to a side of the third direction DR3, which is thedisplay direction, and the term “top surface” refers to a surface towardthe side of the third direction DR3. Further, the term “downward” refersto the other side in the third direction DR3, which is an oppositedirection to the display direction, and the term “bottom surface” refersto a surface toward the other side of the third direction DR3.Furthermore, “left”, “right”, “upper” and “lower” indicate directionswhen the display device 10 is viewed from above. For example, “rightside” indicates a side of the first direction DR1, “left side” indicatesthe other side of the first direction DR1, “upper side” indicates a sideof the second direction DR2, and “lower side” indicates the other sideof the second direction DR2.

The display device 10 may include the display area DPA and a non-displayarea NDA. The display area DPA is an area where a screen can bedisplayed, and the non-display area NDA is an area where a screen is notdisplayed.

The shape of the display area DPA may follow the shape of the displaydevice 10. For example, the shape of the display area DPA may have arectangular shape similar to the overall shape of the display device 10in plan view. The display area DPA may substantially occupy the centerof the display device 10.

The display area DPA may include pixels PX. The pixels PX may bearranged in a matrix. The shape of each pixel PX may be a rectangular orsquare shape in plan view. Each pixel PX may include a light emittingelements made of inorganic particles.

The non-display area NDA may be disposed around the display area DPA.The non-display area NDA may completely or partially surround thedisplay area DPA. The non-display area NDA may form a bezel of thedisplay device 10.

FIG. 2 is a schematic plan view illustrating a pixel of a display deviceaccording to an embodiment. FIG. 3 is a schematic cross-sectional viewillustrating an example taken along line of FIG. 2.

Referring to FIG. 2, each pixel PX of the display device 10 may includean emission area EMA and a non-emission area. The emission area EMA maybe defined as an area in which light emitted from a light emittingelement 30 is emitted, and the non-emission area may be defined as anarea in which light is not emitted because the light emitted from thelight emitting element 30 does not reach.

The emission area EMA may include an area in which the light emittingelement 30 is disposed and an area adjacent thereto. The emission areamay also include a region in which the light emitted from the lightemitting element 30 is reflected or refracted by another member andemitted.

Each pixel PX may further include a cutout area CBA disposed in thenon-emission area. The cutout area CBA may be disposed at the upper side(or a side in the second direction DR2) from the emission area EMAwithin a pixel PX. The cutout area CBA may be disposed between theemission areas EMA of the pixels PX disposed adjacent to each other inthe second direction DR2.

The cutout area CBA may be a region in which electrodes 21 and 22included in each of the pixels PX adjacent to each other along thesecond direction DR2 are separated. The electrodes 21 and 22 provided ineach pixel PX are separated in the cutout area CBA, and a part of theelectrodes 21 and 22 provided in each pixel PX may be disposed in thecutout area CBA. The light emitting element 30 may not be disposed inthe cutout area CBA.

Referring to FIGS. 2 and 3, the display device 10 may include asubstrate SUB, a circuit element layer PAL disposed on the substrateSUB, and a light emitting element layer EML disposed on the circuitelement layer PAL. The light emitting element layer EML may include afirst bank 40, first and second electrodes 21 and 22, a second bank 60,a light emitting element 30, first and second contact electrodes 26 and27, insulating layers 51, 52, 53, and 54, and a filler 55.

The substrate SUB may be an insulating substrate. The substrate SUB maybe made of an insulating material such as glass, quartz, or polymerresin. The substrate SUB may be a rigid substrate, but may also be aflexible substrate which can be bent, folded, or rolled.

The circuit element layer PAL may be disposed on the substrate SUB. Thecircuit element layer PAL may include at least one transistor and thelike to drive the light emitting element layer EML.

The first bank 40 may be disposed on the circuit element layer PAL.Although not shown in the drawings, the circuit element layer PAL mayinclude a via layer, and the first bank 40 may be disposed on the vialayer of the circuit element layer PAL.

The first bank 40 may have a shape extending in the second direction DR2within each pixel PX in plan view. The first bank 40 may end while beingseparated within the emission area EMA partitioned by the second bank 60so that the first bank 40 does not extend to the adjacent pixel PX inthe second direction DR2.

The first bank 40 may include a first sub-bank 41 and a second sub-bank42. The first sub-bank 41 and the second sub-bank 42 may be spaced apartfrom each other and disposed to face each other in the first directionDR1. For example, the first sub-bank 41 may be disposed on the left sideof the emission area EMA in plan view, and the second sub-bank 42 may bedisposed on the right side of the emission area EMA in plan view. Thespace between the first and second sub-banks 41 and 42 spaced apart fromeach other may provide an area where light emitting elements 30 aredisposed.

The first and second sub-banks 41 and 42 may each have a structure inwhich at least a part protrudes from the top surface of the substrateSUB. The protruding parts of the first and second sub-banks 41 and 42may have inclined side surfaces.

The first sub-bank 41 may include a top surface 41US, a bottom surface41BS and a side surface 41SS. The bottom surface 41BS of the firstsub-bank 41 may be placed on a surface of the circuit element layer PAL.The top surface 41US of the first sub-bank 41 may face the bottomsurface 41BS of the first sub-bank 41.

The side surface 41SS of the first sub-bank 41 may include a first sidesurface 41SS1 and a second side surface 41SS2. The first side surface41SS1 of the first sub-bank 41 may be a side surface located on a sidefacing the second sub-bank 42 in a pixel PX, and the second side surface41SS2 of the first sub-bank 41 may be a side surface located on theother side opposite to a side facing the second sub-bank 42. The firstside surface 41SS1 of the first sub-bank 41 may face the second sub-bank42 and/or the light emitting element 30, and the second side surface41SS2 of the first sub-bank 41 may face the second bank 60.

The side surface 41SS of the first sub-bank 41 may be inclined at anangle with respect to the bottom surface 41BS of the first sub-bank 41.As the first sub-bank 41 includes the inclined side surface 41SS, thefirst sub-bank 41 may change the traveling direction of light emittedfrom the light emitting element 30 and proceeding to the side surface41SS of the first sub-bank 41, for example, the first side surface 41SS1of the first sub-bank 41, to the third direction DR3 (for example, theupward direction or the display direction).

Similarly, the second sub-bank 42 may include a top surface 42US, abottom surface 42BS and a side surface 42SS. The bottom surface 42BS ofthe second sub-bank 42 may be placed on a surface of the circuit elementlayer PAL. The top surface 42US of the second sub-bank 42 may face thebottom surface 42BS of the second sub-bank 42.

The side surface 42SS of the second sub-bank 42 may include a first sidesurface 42SS1 and a second side surface 42SS2. The first side surface42SS1 of the second sub-bank 42 may be a side surface located on a sidefacing the first sub-bank 41 in a pixel PX, and the second side surface42SS2 of the second sub-bank 42 may be a side surface located on theother side opposite to the side facing the first sub-bank 41. The firstside surface 42SS1 of the second sub-bank 42 may face the first sub-bank41 and/or the light emitting element 30, and the second side surface42SS2 of the second sub-bank 42 may face the second bank 60.

The side surface 42SS of the second sub-bank 42 may be inclined at anangle with respect to the bottom surface 42BS of the second sub-bank 42.As the second sub-bank 42 includes the inclined side surface 42SS, thesecond sub-bank 42 may change the traveling direction of light emittedfrom the light emitting element 30 and proceeding to the side surface42SS of the second sub-bank 42, for example, the first side surface42SS1 of the second sub-bank 42, to the third direction DR3 (forexample, the upward direction or the display direction).

Although the side surface of the first bank 40 is inclined in a linearshape in the drawings, the shape of the side surface of the first bank40 is not limited thereto. For example, the side surface or the outersurface of the first bank 40 may have a curved semicircle or a halfellipse shape. In an embodiment, the first bank 40 may include anorganic insulating material such as polyimide (PI), but is not limitedthereto.

The first and second electrodes 21 and 22 may be disposed on the firstbank 40. The first electrode 21 may be disposed on the first sub-bank 41and the second electrode 22 may be disposed on the second sub-bank 42.

A voltage from the circuit element layer PAL may be applied to the firstand second electrodes 21 and 22 so that the light emitting element 30may emit light. During the manufacturing process of the display device10, an alignment signal may be applied to the first and secondelectrodes 21 and 22 to form an electric field for aligning the lightemitting elements 30. The first and second electrodes 21 and 22 maychange the traveling direction of the light proceeding in the lateraldirection among the lights emitted from the light emitting element 30 tothe third direction DR3 (the upward direction or the display direction).Hereinafter, in the specification, the first electrode 21 and the secondelectrode 22 may be referred to as a first reflective electrode 21 and asecond reflective electrode 22, respectively.

In an embodiment, each of the first and second electrodes 21 and 22 mayinclude a conductive material having high reflectivity. For example,each of the first and second electrodes 21 and 22 may include metalssuch as silver (Ag), copper (Cu), aluminum (Al), gold (Au), platinum(Pt), palladium (Pd), indium (In), nickel (Ni), or chrome (Cr), oralloys of such metals. The structure of the first and second electrodes21 and 22 may include multiple layers of such materials formed intointegral structures. However, the disclosure is not limited thereto, andthe structure of each of the first and second electrodes 21 and 22 mayinclude one or more layers of a transparent conductive material and amaterial having high reflectivity stacked with each other, or may beformed as a single layer including these materials. For example, each ofthe first and second electrodes 21 and 22 may have a stacked structuresuch as ITO/Ag/ITO, ITO/Ag/IZO, or ITO/Ag/ITZO/IZO.

Each of the first electrode 21 and the second electrode 22 may have ashape extending in the second direction DR2 in plan view. The firstelectrode 21 and the second electrode 22 may be spaced apart from eachother and disposed to face each other in the first direction DR1. Thefirst electrode 21 and the second electrode 22 may have a shape similarto the planar shape of the first sub-bank 41 and the second sub-bank 42to fully cover the first sub-bank 41 and the second sub-bank 42 in planview, but may have a larger area.

The first electrode 21 may extend in the second direction DR2 in planview so as to overlap a part of the second bank 60 extending in thefirst direction DR1. The first electrode 21 may be electricallyconnected to the circuit element layer PAL through a first contact holeCT1.

The second electrode 22 may extend in the second direction DR2 in planview so as to overlap a part of the second bank 60 extending in thefirst direction DR1. The second electrode 22 may be electricallyconnected to the circuit element layer PAL through a second contact holeCT2.

The first electrode 21 and the second electrode 22 may be separated fromthe first and the second electrodes 21 and 22 of the neighboring pixelPX in the second direction DR2 in the cutout area CBA in the pixel PX,respectively. The planar shape of the first electrode 21 and the secondelectrode 22 separated in the cutout area CBA may be formed by cuttingthe first and second electrodes 21 and 22 in the cutout area CBA afterdisposing the light emitting element 30 during the manufacturing processof the display device 10. However, the disclosure is not limitedthereto, and a part of the first and second electrodes 21 and 22 mayextend to a neighboring pixel in the second direction DR2 and beintegrated with the electrode of the neighboring pixel and only one ofthe first electrode 21 or the second electrode 22 may be separated inthe cutout area CBA.

The first electrode 21 may be placed on the outer surface of the firstsub-bank 41. The first electrode 21 may fully cover the top surface 41USand the side surface 41SS of the first sub-bank 41. The first electrode21 may extend to the outer side from the first and second side surfaces41SS1 and 41SS2 of the first sub-bank 41 to also be partially disposedon a surface of the circuit element layer PAL exposed by the first andsecond sub-banks 41 and 42.

The second electrode 22 may be placed on the outer surface of the secondsub-bank 42. The second electrode 22 may fully cover the top surface42US and the side surface 42SS of the second sub-bank 42. The secondelectrode 22 may extend to the outer side from the first and second sidesurfaces 42SS1 and 42SS2 of the second sub-bank 42 to also be partiallydisposed on a surface of the circuit element layer PAL exposed by thefirst and second sub-banks 41 and 42.

The top surface 21US (or the surface) of the first electrode 21 may notbe flat. The top surface 21US of the first electrode 21 may include atextured surface (or surface irregularities). The top surface 21US ofthe first electrode 21 may include an textured surface and the topsurface 21US of the first electrode 21 may have a surface roughness. Thetextured surface of the top surface 21US may provide a surfaceroughness. In the specification, the surface roughness may be defined asthe degree of fine irregularities (i.e., the degree of roughness) thatoccur on the surface. Although in the drawing, the entire top surface21US of the first electrode 21 disposed on the first sub-bank 41includes a textured surface, the disclosure is not limited thereto. Forexample, the textured surface may be formed on a partial region of thetop surface 21US of the first electrode 21.

Similarly, a top surface 22US of the second electrode 22 may not beflat. The top surface 22US of the second electrode 22 may include atextured surface. As the top surface 22US of the second electrode 22includes an textured surface, the top surface 22US of the secondelectrode 22 may have a surface roughness. The textures surface of thetop surface 22US may provide a surface roughness. Although it isillustrated in the drawing that the entire top surface 22US of thesecond electrode 22 disposed on the second sub-bank 42 includes antextured surface, the disclosure is not limited thereto. For example,the textured surface may be formed on a partial region of the topsurface 22US of the second electrode 22.

The first and second electrodes 21 and 22 may be electrically connectedto the light emitting elements 30 to apply a voltage to the lightemitting elements 30 for light emission. For example, the electrodes 21and 22 may be electrically connected to the light emitting element 30disposed between the first electrode 21 and the second electrode 22 (andthe light emitting element 30 and the first and second electrodes 21 and22 may be spaced apart from each other) through first and second contactelectrodes 26 and 27, and an electrical signal applied to the electrodes21 and 22 may be transmitted to the light emitting element 30 throughthe contact electrodes 26 and 27.

The first insulating layer 51 may be disposed on the first and secondelectrodes 21 and 22. The first insulating layer 51 may be disposed onthe first electrode 21 and the second electrode 22 and expose at least apart of the first electrode 21 and the second electrode 22. The firstinsulating layer 51 may be formed entirely on a surface of the substrateSUB including the region between the first electrode 21 and the secondelectrode 22, but a part of the first electrode 21 and the secondelectrode 22 may be exposed in the region overlapping the top surface41US of the first sub-bank 41 and the top surface 42US of the secondsub-bank 42 in the third direction DR3.

The first insulating layer 51 may be formed to have a step such that apart of the top surface is recessed between the first electrode 21 andthe second electrode 22 (forming a recessed surface between the firstelectrode 21 and the second electrode 22). The first insulating layer 51may be formed such that a part of its top surface is recessed due to astep formed by a member (for example, the first electrode 21 and/or thesecond electrode 22) disposed thereunder. In some embodiments, an emptyspace may be formed between the light emitting element 30 and the topsurface of the first insulating layer 51, a part of which is recesseddue to the step formed between the first electrode 21 and the secondelectrode 22. The recessed portion of the first insulating layer 51 maybe the portion where the first electrode 21 and second electrode 22 arenot disposed under the first insulating layer 51. A material forming asecond insulating layer 52 which will be described later may fill theempty space between the first insulating layer 51 and the light emittingelement 30. However, the disclosure is not limited thereto, and thefirst insulating layer 51 may not have a step between the firstelectrode 21 and the second electrode 22. For example, the firstinsulating layer 51 may include a flat top surface to dispose the lightemitting element 30 between the first electrode 21 and the secondelectrode 22.

The first insulating layer 51 may protect the first electrode 21 and thesecond electrode 22 while insulating them from each other. It ispossible to prevent the light emitting element 30 disposed on the firstinsulating layer 51 from being damaged by direct contact with othermembers.

The second bank 60 may be disposed on the first insulating layer 51. Thesecond bank 60 may be disposed in the form of a grid pattern includingportions extending in the first and second directions DR1 and DR2 inplan view. The second bank 60 may be disposed across the boundary ofeach of the pixels PX to delimit the neighboring pixels PX.

The second bank 60 may have a height greater than that of the first bank40. The second bank 60 may prevent ink from overflowing to adjacentpixels PX during an inkjet printing process for aligning the lightemitting elements 30 in the manufacturing process of the display device10. Further, the second bank 60 may be disposed to surround the emissionarea EMA and the cutout area CBA disposed for each pixel PX to delimitthem from each other. In an embodiment, the second bank 60 may includean organic insulating material such as polyimide (PI), but is notlimited thereto.

The light emitting element 30 may be disposed on the first insulatinglayer 51 between the first electrode 21 and the second electrode 22. Thelight emitting element 30 may have a shape extending in a substantiallyperpendicular direction to the first and second electrodes 21 and 22.However, the disclosure is not limited thereto. Some of the lightemitting elements 30 may be arranged in a substantially perpendiculardirection to the first and second electrodes 21 and 22, and other lightemitting elements 30 may be arranged in an oblique angle to the firstand second electrodes 21 and 22.

The second insulating layer 52 may be partially disposed on the lightemitting element 30 disposed between the first electrode 21 and thesecond electrode 22. The second insulating layer 52 may be disposed topartially surround the outer surface of the light emitting element 30.The second insulating layer 52 may be disposed on the light emittingelement 30 to expose both ends of the light emitting element 30. Thesecond insulating layer 52 may function to protect the light emittingelement 30 and also fix the light emitting element 30 in a manufacturingprocess of the display device 10.

Although not shown in the drawings, the material constituting the secondinsulating layer 52 may be disposed between the first electrode 21 andthe second electrode 22, and fill the empty space between the lightemitting element 30 and the first insulating layer 51 formed by thedepression (or recessed step portion) as described above.

The first and second contact electrodes 26 and 27 may be disposed on thesecond insulating layer 52. The first and second contact electrodes 26and 27 may have a shape extending in the second direction DR2 in planview, respectively. The first contact electrode 26 and the secondcontact electrode 27 may be spaced apart from each other and disposed toface each other in the first direction DR1.

The first and second contact electrodes 26 and 27 may contact the lightemitting element 30 and the electrodes 21 and 22, respectively. Thefirst contact electrode 26 may be disposed on the first electrode 21 andthe second contact electrode 27 may be disposed on the second electrode22. The first contact electrode 26 may contact an end of the lightemitting element 30 while contacting the top surface 21US of the firstelectrode 21 exposed by the first insulating layer 51. The secondcontact electrode 27 may contact the other end of the light emittingelement 30 while contacting the top surface 22US of the second electrode22 exposed by the first insulating layer 51.

The first contact electrode 26 and the second contact electrode 27 mayinclude a textured surface on a part of the bottom surface. The bottomsurface of the first contact electrode 26 may include a textured surfacein the region contacting the first electrode 21, and may be flat in theregion not contacting the first electrode 21. Similarly, the bottomsurface of the second contact electrode 27 may include a texturedsurface in the region contacting the second electrode 22, and may beflat in the region not contacting the second electrode 22. The first andsecond contact electrodes 26 and 27 may have flat top surfaces.

The end of the light emitting element 30 exposed by the secondinsulating layer 52 may be electrically connected to the first electrode21 through the first contact electrode 26 and the other end may beelectrically connected to the second electrode 22 through the secondcontact electrode 27.

A third insulating layer 53 may be disposed on the first contactelectrode 26. The third insulating layer 53 may electrically insulatethe first contact electrode 26 and the second contact electrode 27 fromeach other. The third insulating layer 53 may be disposed to completelycover the first contact electrode 26, but may not be disposed on theother end of the light emitting element 30 so that the light emittingelement 30 can contact the second contact electrode 27.

The second contact electrode 27 may be disposed on the second electrode22, the second insulating layer 52, and the third insulating layer 53.The second contact electrode 27 may extend to the side of the secondinsulating layer 52 and the third insulating layer 53 from the other endof the light emitting element 30 to also be partially disposed on thethird insulating layer 53.

The first and second contact electrodes 26 and 27 may include aconductive material. For example, it may include ITO, IZO, ITZO,aluminum (Al), or the like. In an embodiment, the first and secondcontact electrodes 26 and 27 may include a transparent conductivematerial, but are not limited thereto.

A fourth insulating layer 54 may be entirely disposed on the substrateSUB. The fourth insulating layer 54 may function to protect the membersdisposed on the substrate SUB against the external environment.

The filler 55 may fill the region partitioned by the second bank 60. Thefiller 55 may protect members included in the light emitting elementlayer EML. The filler 55 is not particularly limited as long as thematerial thereof does not damage members disposed below whiletransmitting light. The filler 55 may be omitted.

FIG. 4 is a schematic diagram of a light emitting element according toan embodiment.

Referring to FIG. 4, the light emitting element 30 which is aparticulate element may have a rod or cylindrical shape having an aspectratio. The length of the light emitting element 30 may be larger thanthe diameter of the light emitting element 30, and the aspect ratio maybe about 3:1 to about 10:1, but the disclosure is not limited thereto.

The light emitting element 30 may have a size of a nanometer scale(equal to or greater than about 1 nm and less than about 1 μm) to amicrometer scale (equal to or greater than about 1 μm and equal to orless than about 1 mm). In an embodiment, both the diameter and thelength of the light emitting element 30 may be on a nanometer scale, oron a micrometer scale. In other embodiments, the diameter of the lightemitting element 30 may be on a nanometer scale, while the length of thelight emitting element 30 may be on a micrometer scale. In someembodiments, some of the light emitting elements 30 may have a diameterand/or length on a nanometer scale, while some others of the lightemitting elements 30 may have a diameter and/or length on a micrometerscale.

In an embodiment, the light emitting element may be an inorganic lightemitting diode. The light emitting element 30 may include asemiconductor layer doped with any conductivity type (e.g., p-type orn-type) impurities. The semiconductor layer may emit light of a specificwavelength band by receiving an electrical signal applied from anexternal power source.

The light emitting element 30 according to an embodiment may include afirst semiconductor layer 31, an active layer 33, a second semiconductorlayer 32, and an electrode layer 37 sequentially stacked with each otherin a longitudinal direction. The light emitting element may furtherinclude an insulating layer 38 covering the outer surfaces of the firstsemiconductor layer 31, the second semiconductor layer 32, and theactive layer 33.

The first semiconductor layer 31 may be, for example, an n-typesemiconductor having a first semiconductor type. The first semiconductorlayer 31 may be doped with a first conductive dopant. For example, thefirst conductive dopant may be Si, Ge, Sn, or the like. In anembodiment, the first semiconductor layer 31 may be n-GaN doped withn-type Si.

The second semiconductor layer 32 may be disposed to be spaced apartfrom the first semiconductor layer 31. The second semiconductor layer 32may be, for example, a p-type semiconductor having a second conductivitytype. The second semiconductor layer 32 may be doped with a secondconductive dopant. For example, the second conductive dopant may be Mg,Zn, Ca, Se, Ba, or the like. In an embodiment, the second semiconductorlayer 32 may be p-GaN doped with p-type Mg.

The active layer 33 may be disposed between the first semiconductorlayer 31 and the second semiconductor layer 32. The active layer 33 mayinclude a material having a single or multiple quantum well structure.The active layer 33 may emit light by coupling of electron-hole pairsaccording to an electrical signal applied through the firstsemiconductor layer 31 and the second semiconductor layer 32. However,the disclosure is not limited thereto, and the active layer 33 may havesemiconductor materials having a large band gap energy alternatelystacked with semiconductor materials having a small band gap energy, andmay include other group III to V semiconductor materials according tothe wavelength band of the emitted light.

The light emitted from the active layer 33 may be projected through theside surfaces as well as the outer surface of the light emitting element30 in the longitudinal direction. The directionality of the lightemitted from the active layer 33 is not limited to one direction.

The electrode layer 37 may be disposed on the second semiconductor layer32. The electrode layer 37 may be an ohmic contact electrode. However,the disclosure is not limited thereto, and the electrode layer 37 may bea Schottky contact electrode.

In the display device 10, when the light emitting element 30 iselectrically connected to an electrode or a contact electrode, theelectrode layer 37 may reduce the resistance between the light emittingelement 30 and the electrode or contact electrode. The electrode layer37 may include conductive metal. For example, the electrode layer 37 mayinclude at least one of aluminum (Al), titanium (Ti), indium (In), gold(Au), silver (Ag), indium tin oxide (ITO), indium zinc oxide (IZO), andindium tin zinc oxide (ITZO). Further, the electrode layer 37 mayinclude an n-type or p-type doped semiconductor material.

The insulating layer 38 is arranged to surround the outer surfaces ofthe semiconductor layers and electrode layers described above. In anembodiment, the insulating layer 38 may surround at least the outersurface of the active layer 33 and extend along the extension directionof the light emitting element 30. The insulating layer 38 may protectthe members. For example, the insulating layer 38 may surround sidesurfaces of the members to expose both ends of the light emittingelement 30 in the longitudinal direction. The insulating layer 38 mayinclude materials having insulating properties. Accordingly, it ispossible to prevent an electrical short circuit that may occur when theactive layer 33 is in direct contact with the electrode through whichthe electrical signal is transmitted to the light emitting element 30.Since the insulating layer 38 includes the active layer 33 to protectthe outer surface of the light emitting element 30, it is possible toprevent degradation in light emission efficiency.

Further, in some embodiments, the insulating layer 38 may have an outersurface which is surface-treated. When the display device 10 ismanufactured, the light emitting elements 30 may be dispersed in an inkand sprayed on the electrodes and then aligned on the electrodes. Here,the surface of the insulating layer 38 may be treated in a hydrophobicor hydrophilic manner in order to prevent the light emitting elements 30from aggregating with other light emitting elements 30 in the ink.

FIG. 5 is an enlarged schematic cross-sectional view illustrating anexample of area A of FIG. 3. FIG. 6A is an enlarged schematiccross-sectional view illustrating a traveling path of light emitted froma light emitting element. FIG. 6B is an enlarged schematiccross-sectional view of area Q of FIG. 6A.

Referring to FIGS. 3 to 5, the top surface 21US of the first electrode21 and the top surface 22US of the second electrode 22 may includesurface irregularities SR, respectively.

The first electrode 21 may include surface irregularities SR (firstsurface irregularities) in the top surface 21US in the regionoverlapping at least the first side surface 41SS1 of the first sub-bank41 in the third direction DR3. Similarly, the second electrode 22 mayinclude surface irregularities SR (second surface irregularities) in thetop surface 22US in the region overlapping at least the first sidesurface 42SS1 of the second sub-bank 42 in the third direction DR3. Inan embodiment, the first electrode 21 may include the surfaceirregularities SR (first surface irregularities) on the entire topsurface 21US in the region overlapping the first side surface 41SS1, thesecond side surface 41SS2 and the top surface 41US of the first sub-bank41 in the third direction DR3. The second electrode 22 may include thesurface irregularities SR (or second surface irregularities) on theentire top surface 22US in the region overlapping the first side surface42SS1, the second side surface 42SS2 and the top surface 42US of thesecond sub-bank 42 in the third direction DR3.

The surface irregularities SR included in the top surface 21US of thefirst electrode 21 and the top surface 22US of the second electrode 22may be formed randomly. In an embodiment, the cross-sectional shape ofthe surface irregularities SR may be an amorphous random shape. However,the disclosure is not limited thereto, and in some embodiments, thecross-sectional shape of the surface irregularities SR may be a polygonsuch as a triangle or a trapezoid, or may have a shape of a part of acircle or an ellipse.

The surface irregularities SR formed on the top surface 21US of thefirst electrode 21 and the top surface 22US of the second electrode 22may be formed by various methods such as a dry etching method and aplasma etching method after the patterning process forming the firstelectrode 21 and the second electrode 22. The surface irregularities SRmay be formed so that the surfaces of the first electrode 21 and thesecond electrode 22, the top surfaces 21US and 22US, may have a surfaceroughness. In an embodiment, the surface irregularities SR formed on thetop surface 21US of the first electrode 21 and the top surface 22US ofthe second electrode 22 may be formed over the entire surface by dryetching after the patterning process for forming the first electrode 21and the second electrode 22.

The first surface irregularities SR formed on the top surface 21US ofthe first electrode 21 and the second surface irregularities SR formedon the top surface 22US of the second electrode 22 may be formedsimultaneously by the same process. Accordingly, the first surfaceirregularities SR formed on the top surface 21US of the first electrode21 and the second surface irregularities SR formed on the top surface22US of the second electrode 22 may have the same surface roughness.

In an embodiment, the first surface irregularities SR formed on the topsurface 21US of the first electrode 21 disposed on the first sub-bank 41may have the same surface roughness for each area on the first sub-bank41. For example, the first electrode 21 may have the same surfaceroughness on the top surface 41US and the first and second side surfaces41SS1 and 41SS2 of the first sub-bank 41. Although the top surface 21USof the first electrode 21 disposed on the first sub-bank 41 is shown ashaving the same surface roughness for each area, the disclosure in notlimited thereto. In other embodiments, the first electrode 21 may have adifferent surface roughness for each area on the first sub-bank 41. Forexample, the surface roughness of the top surface 21US of the firstelectrode 21 in the region overlapping the top surface 41US of the firstsub-bank 41 may be different from the surface roughness of the topsurface 21US of the first electrode 21 in the region overlapping theside surface 41SS of the first sub-bank 41. The first electrode 21disposed on the first sub-bank 41 by the inclined side surface 41SS ofthe first sub-bank 41 to form the surface irregularities SR may beformed to have different surface roughness for each area.

The surface irregularities SR formed in the first and second electrodes21 and 22 may irregularly reflect (or diffusely reflect) the lightemitted from the light emitting element 30 and proceeding to the topsurfaces 21US and 22US of the first and second electrodes 21 and 22. Asdescribed above, the first and second electrodes 21 and 22 may include amaterial having high reflectivity, and each of the top surfaces 21US and22US of the first and second electrodes 21 and 22 may be a reflectivesurface reflecting the light emitted from the light emitting element 30and incident thereon. Each reflective surface (or the top surfaces 21USand 22US) of the first and second electrodes 21 and 22 includes randomsurface irregularities SR, the light emitted from the light emittingelement 30 and incident on the first and second electrodes 21 and 22 maybe diffusely reflected in multiple directions from the reflectivesurfaces 21US and 22US. The light incident on the reflective surfaces21US and 22US of the first and second electrodes 21 and 22 may bediffusely reflected in various directions by the surface irregularitiesSR formed on the reflective surfaces 21US and 22US of the first andsecond electrodes 21 and 22 to proceed to layers disposed on the firstand second electrodes 21 and 22 with various incident angles.

As described above, the traveling direction of the light emitted fromthe light emitting element 30 is not limited to one direction. The lightemitted from the light emitting element 30 may be emitted from both endsof the light emitting element 30 to proceed to the first side surface41SS1 of the first sub-bank 41 and the first side surface 41SS2 of thesecond sub-bank 42, and may be emitted from the side surface of thelight emitting element 30 to proceed to the top or bottom portion of thedisplay device 10.

A part of the light emitted from the light emitting element 30 toproceed to the first side surfaces 41SS1 and 42SS1 of the first andsecond sub-banks 41 and 42 may pass through the layers disposed on thefirst and second electrodes 21 and 22 to be emitted to the outside, andanother part of the light may not pass through the layers disposed onthe first and second electrodes 21 and 22 and may not be emitted to theoutside. For example, part of the light emitted from the light emittingelement 30 may be emitted to the outside of the light emitting elementlayer EML, but the other part thereof may not be emitted to the outsideof the light emitting element layer EML and may disappear within thelight emitting element layer EML. For example, an optical waveguide maybe formed by the layers disposed on the first and second electrodes 21and 22 in the adjacent area of the light emitting element 30, and a partof the light emitted from the light emitting element 30 to proceed tothe side surface of the first bank 40 may not be emitted to the outsideof the light emitting element layer EML due to the optical waveguide.The optical waveguide may be formed when total reflection occurs due toa difference in refractive indices of the layers disposed in the regionadjacent to the light emitting element 30. As an example, totalreflection may occur when the refractive index of at least one of thelayers (i.e., the first contact electrode 26, the second contactelectrode 27, the third insulating layer 53 or the fourth insulatinglayer 54) disposed on the first and second electrodes 21 and 22 may begreater than the refractive index of the filler 55. A part of the lightemitted from the light emitting element 30 may be kept within the layersdue to the optical waveguide formed by the layers disposed on the firstand second electrodes 21 and 22. Such light may be converted to heatenergy, or may be absorbed by other layers and disappear. Accordingly,since the light emitted from the light emitting element 30 is notemitted to the outside of the light emitting element layer EML, thelight emission efficiency of the display device 10 may be reduced. Themain reason for the formation of the optical waveguide which may reducethe light emission efficiency of the display device 10 may be totalreflection occurring due to the difference in refractive indices of thelayers disposed on the first and second electrodes 21 and 22.Accordingly, the light emission efficiency of the display device 10 maybe increased by reducing the rate of occurrence of the total reflection.In an embodiment, the refractive indices of the third insulating layer53 and the fourth insulating layer 54 may be different from therefractive indices of the first contact electrode 26 and the secondcontact electrode 27. In an embodiment, the refractive indices of thethird insulating layer 53 and the fourth insulating layers 54 may besmaller than the refractive indices of the first contact electrode 26and the second contact electrode 27. In an embodiment, the refractiveindex of the filler 55 may be smaller than the refractive indices of thefirst contact electrode 26 and the second contact electrode 27. Thedisplay device 10 according to an embodiment may form the surfaceirregularities SR on the top surfaces 21US and 22US of the first andsecond electrodes 21 and 22 to diffusely reflect the light in a randomdirection, thereby inducing various incident angles of the lightincident on the layers. Accordingly, by inducing various incident anglesof the light incident on the layers, a ratio of light incident at anangle equal to or greater than a critical angle at which totalreflection may occur to light incident on the layers may be reduced,thereby reducing the formation rate of the optical waveguide.

Hereinafter, the path in which the light emitted from the light emittingelement 30 proceeds to the insulating layers and/or the contactelectrodes 26 and 27 will be described in more detail with reference toFIGS. 6A and 6B.

As described above, the light generated from the active layer 33 of thelight emitting element 30 may be emitted randomly withoutdirectionality. Referring to FIG. 6A, the light emitted from the lightemitting element 30 may include a first light L1, a second light L2 anda third light L3 according to a schematic light traveling direction. Thefirst light L1 may be light traveling upward, i.e., in the thirddirection DR3, from the light emitting element 30. The second light L2may be light traveling laterally, i.e., toward the first surfaces 41SS1and 42SS1 of the first and second sub-banks 41 and 42, from the lightemitting element 30. The third light L3 may be light traveling downward,i.e., in the opposite direction of the third direction DR3, from thelight emitting element 30.

The first light L1 may travel upward from the light emitting element 30and pass through the second insulating layer 52, the first and secondcontact electrodes 26 and 27, the third insulating layer 53, and thefourth insulating layer 54 disposed on the light emitting element 30 tobe emitted to the filler 55. As shown in the drawing, most of the firstlight L1 traveling upward from the light emitting element 30 may beemitted to, for example, the filler 55 without being totally reflectedbecause its incident angle at the interface between the filler 55 andthe fourth insulating layer 54 is smaller than the critical angle atwhich total reflection occurs. Accordingly, the light emission ratio ofthe first light L1 may be large.

The second light L2 may travel laterally from the light emitting element30 to proceed toward the first surfaces 41S Si and 42S Si of the firstand second sub-banks 41 and 42 facing both ends of the light emittingelement 30.

A part of the second light L2 may proceed toward the first side surface41SS1 of the first sub-bank 41. The second light L2 proceeding towardthe first side surface 41SS1 of the first sub-bank 41 may pass throughthe first and third insulating layers 51 and 53 and the first contactelectrode 26 to proceed toward the reflective surface 21US of the firstelectrode 21 disposed on the first side surface 41SS1 of the firstsub-bank 41. The second light L2 may be diffusely reflected from thereflective surface 21US of the first electrode 21 by the surfaceirregularities SR formed on the reflective surface 21US of the firstelectrode 21. Accordingly, by randomly changing the direction of thereflected light, the ratio at which the total reflection occurs in thelayers disposed on the first electrode 21 may be reduced. As a result,by reducing the occurrence ratio of the total reflection, the ratio atwhich the second light L2 is not emitted to the outside due to theoptical waveguide may be reduced.

Similarly, the other part of the second light L2 may proceed toward thefirst side surface 42SS1 of the second sub-bank 42. The second light L2proceeding toward the side of the first side surface 42SS1 of the secondsub-bank 42 may pass through the first insulating layer 51 and thesecond contact electrode 27 to proceed toward the reflective surface22US of the second electrode 22 disposed on the first side surface 42SS1of the second sub-bank 42. The second light L2 may be diffuselyreflected from the reflective surface 22US of the second electrode 22 bythe surface irregularities SR formed on the reflective surface 22US ofthe second electrode 22. Accordingly, by randomly changing the directionof the reflected light, the ratio at which the total reflection occursin the layers disposed on the second electrode 22 may be reduced. As aresult, by reducing the occurrence ratio of the total reflection, theratio at which the second light L2 is not emitted to the outside by theoptical waveguide may be reduced.

The third light L3 may proceed toward the first insulating layer 51 andthe circuit element layer PAL disposed below the light emitting element30. Most of the third light L3 proceeding toward the first insulatinglayer 51 and the circuit element layer PAL may be absorbed by themembers and disappear. However, the disclosure is not limited thereto,and a part of the third light L3 may be reflected to proceed in thedisplay direction DR3.

Referring to FIG. 6B, a light L21 which is a part of the second light L2emitted from the light emitting element 30 and proceeding laterally mayproceed toward the fourth insulating layer 54. The light L21 proceedingtoward the fourth insulating layer 54 may be incident on the interfacebetween the fourth insulating layer 54 and the filler 55. The refractiveindex of the fourth insulating layer 54 and the refractive index of thefiller 55 may be different from each other. When the refractive index ofthe medium is changed at the interface (for example, the top surface ofthe fourth insulating layer 54) reached by the incident light, anoptical interface may be formed. When the optical interface is formed,the light L21 incident toward the interface between the fourthinsulating layer 54 and the filler 55 may be refracted or reflected. Theproceeding direction of the light L21 incident toward the interface ofthe fourth insulating layer 54 and the filler 55 may be determinedaccording to an incident angle θ. For example, when the incident angle θis smaller than the critical angle (the incident angle at which totalreflection starts to occur), at least a part of the light L21 may berefracted at the interface to pass through the interface and thenproceed toward the filler 55. When the incident angle θ is the same asthe critical angle, the light L21 may proceed along the interface, thatis the top surface of the fourth insulating layer 54. When the incidentangle θ is greater than the critical angle, the light L21 may be totallyreflected at the interface to proceed toward the fourth insulating layer54. FIG. 6B illustrates, by way of example, a case where the incidentangle θ of the light L21 proceeding to the fourth insulating layer 54 islarger than the critical angle.

When the light L21 proceeding to the fourth insulating layer 54 isincident at the incident angle θ greater than the critical angle, thelight L21 may be totally reflected at the interface between the fourthinsulating layer 54 and the filler 55. A light L22 totally reflected atthe interface between the fourth insulating layer 54 and the filler 55may be incident on the top surface 22US of the second electrode 22. Thelight L22 totally reflected and incident on the top surface 22US of thesecond electrode 22 may be diffusely reflected in various directions bythe surface irregularities SR formed on the top surface 22US of thesecond electrode 22 as described above. Accordingly, a light L23diffusely reflected from the top surface 22US of the second electrode 22by the surface irregularities SR may have various reflection angles andproceed toward the fourth insulating layer 54. Therefore, as the lightL23 diffusely reflected from the top surface 22US of the secondelectrode 22 is diffusely reflected with various reflection angles, aratio of light incident at an incident angle greater than the criticalangle to the light proceeding toward the fourth insulating layer 54 maybe reduced. Accordingly, no more total reflection may occur at theinterface between the fourth insulating layer 54 and the filler 55. As aresult, the ratio at which the light is not emitted to the outside bythe optical waveguide may be reduced.

According to the embodiment described above, by forming random surfaceirregularities SR on the top surfaces 21US and 22US (or reflectivesurfaces) of the first electrode 21 and the second electrode 22, thelight incident on the top surfaces 21US and 22US of the first and secondelectrodes 21 and 22 may be diffusely reflected and the light travelingdirection may be randomly changed. Therefore, by randomly changing thelight traveling direction, the occurrence ratio of the total reflectionwhich may occur due to the difference in refractive indices between theplurality of layers may be reduced, thereby reducing the formation rateof the optical waveguide. Accordingly, the light loss caused by theoptical waveguide may be reduced to increase the light emissionefficiency of the display device 10.

As the surface irregularities SR are formed on the top surfaces 21US and22US of the first and second electrodes 21 and 22, the surface area ofthe first and second electrodes 21 and 22 may increase. Accordingly, thesurface area of the first and second electrodes 21 and 22 may increaseto reduce the resistance of the first and second electrodes 21 and 22which transmit an electrical signal from the circuit element layer PAL,thereby increasing the reliability of the display device.

The heat generated within the display device 10, for example, the heatgenerated when the light emitting element 30 emits light, may have aheat dissipation path in which heat is diffused to the first and secondelectrodes 21 and 22 via the contact electrodes 26 and 27 through theportion in which the contact electrodes 26 and 27 and the light emittingelement 30 are in physical contact. For example, the heat energy emittedfrom the light emitting element 30 may be dissipated through the firstand second electrodes 21 and 22. As the surface irregularities SR areformed on the top surfaces 21US and 22US of the first and secondelectrodes 21 and 22, the surface areas of the first and secondelectrodes 21 and 22 increase to increase the heat dissipation area,thereby increasing the heat dissipation efficiency.

Hereinafter, other embodiments will be described. In the followingdescriptions, components that have been previously described will beomitted or simplified to avoid repetition, and differences will bedescribed.

FIG. 7 is a schematic cross-sectional view illustrating another exampletaken along line of FIG. 2. FIG. 8 is a schematic cross-sectional viewillustrating still another example taken along line of FIG. 2.

Embodiments of FIGS. 7 and 8 are different from the embodiment of FIG. 3in that the surface irregularities formed on the top surfaces of thefirst and second electrodes are formed only in a partial region of thefirst and second electrodes.

Referring to FIG. 7, a first electrode 21_1 may have surfaceirregularities only in the region overlapping the first side surface41SS1 of the first sub-bank 41 in the third direction DR3. Similarly, asecond electrode 22_1 may have surface irregularities only in the regionoverlapping the first side surface 42SS1 of the second sub-bank 42 inthe third direction DR3. In the embodiment, even though the surfaceirregularities SR are formed only on a partial region of the firstelectrode 21_1 and the second electrode 22_1, on the first side surfaces41SS1 and 41SS2 of the first and second sub-banks 41 and 42, most of thelight emitted from the light emitting element 30 to proceed laterallymay be diffusely reflected by the surface irregularities SR of the firstand second electrodes 21_1 and 22_1 disposed on the first and secondside surfaces 41SS1 and 42SS1 of the first and second sub-banks 41 and42. Accordingly, even though the surface irregularities SR are formedonly in a partial region, most of the light is diffusely reflected toreduce the formation rate of the optical waveguide, thereby improvingthe light emission efficiency of the display device 10.

Referring to FIG. 8, it is different from the embodiment of FIG. 3 inthat surface irregularities formed on top surfaces 21US_2 and 22US_2 offirst and second electrodes 21_2 and 22_2 are formed only in a partialregion. The first electrode 21_2 may have surface irregularities only inthe region overlapping the first side surface 41SS1 and the top surface41US of the first sub-bank 41 in the third direction DR3. Similarly, thesecond electrode 22_2 may have surface irregularities only in the regionoverlapping the first side surface 42SS1 and the top surface 42US of thesecond sub-bank 42 in the third direction DR3. For example, the firstand second electrodes 21_2 and 22_2 may not include the surfaceirregularities SR in the region overlapping the second side surfaces41SS2 and 42SS2 of the first and second sub-banks 41 and 42 in the thirddirection DR3, respectively.

In the embodiment, since the ratio of the light emitted from the lightemitting element 30 to proceed to the second side surfaces 41SS2 and42SS2 of the first and second sub-banks 41 and 42 is relatively small,the light emission efficiency of the display device 10 may be improvedeven though the surface irregularities SR are not formed in a partialregion of the first electrode 21_2 and the second electrode 22_2overlapping the second side surfaces 41SS2 and 42SS2 of the first andsecond sub-banks 41 and 42 in the third direction DR3.

FIG. 9 is a schematic cross-sectional view illustrating another exampletaken along line of FIG. 2.

Referring to FIG. 9, it is different from the embodiment of FIG. 3 inthat surface irregularities are also formed in a partial region of asurface of the circuit element layer PAL.

A surface PAL_US of the circuit element layer PAL on which the first andsecond sub-banks 41 and 42 are disposed may include a first regionPAL_US1 overlapping the first and second electrodes 21 and 22 in thethird direction DR3 and a second region PAL_US2 not overlapping thefirst and second electrodes 21 and 22 in the third direction DR3.Surface irregularities may be formed on the surface PAL_US of thecircuit element layer PAL not overlapping the first and secondelectrodes 21 and 22, the second region PAL_US2. The surface roughnessof the second region PAL_US2 of the circuit element layer PAL may bedifferent from the surface roughness of the first and second electrodes21 and 22. For example, the surface roughness of the second regionPAL_US2 of the circuit element layer PAL may be smaller than the surfaceroughness of the first and second electrodes 21 and 22.

After a patterning process for forming the first and second electrodes21 and 22, the surface irregularities formed on the surface PAL_US ofthe circuit element layer PAL may be formed in an etching process forforming the surface irregularities SR on the top surfaces 21US and 22USof the first and second electrodes 21 and 22. For example, when a frontetching process is performed in the etching process for formingirregularities on the surfaces of the first and second electrodes 21 and22, the surface PAL_US of the circuit element layer PAL exposed by thefirst and second electrodes 21 and 22, the second region PAL_US2 mayalso be etched to have a surface with the surface roughness.

FIG. 10 is an enlarged schematic cross-sectional view illustratinganother example of area A of FIG. 3. FIG. 11 is an enlarged schematiccross-sectional view of area B of FIG. 10.

Referring to FIGS. 10 and 11, the display device according to theembodiment is different from the embodiment of FIG. 5 in that surfaceirregularities SR_1 formed on the top surface thereof have a constantpattern.

The patterned surface irregularities SR_1 may be formed on top surfaces21US_3 and 22US_3 of first and second electrodes 21_3 and 22_3. Thesurface irregularities SR_1 may be formed repetitively on the topsurfaces 21US_3 and 22US_3 of the first and second electrodes 21_3 and22_3 with a constant period and size. After performing a patterningprocess of the first and second electrodes 21_3 and 22_3, the surfaceirregularities SR_1 formed on the top surfaces 21US_3 and 22US_3 of thefirst and second electrodes 21_3 and 22_3 may be formed using nanospherelithography, E-beam lithography, block copolymer lithography, or thelike.

The cross-sectional shape of the patterned surface irregularities SR_1may be a polygonal shape such as a triangle, a quadrilateral or atrapezoid having a constant size, or may be a part of a circular orelliptical shape. Although it is illustrated in the drawing that thecross-sectional shape of the surface irregularities SR_1 is aquadrilateral, it is not limited thereto. The surface irregularitiesSR_1 may have a constant width W1 and may be formed at a constantinterval W2. The width W1 of the surface irregularities SR_1 and theinterval W2 between the surface irregularities SR_1 may be the samealthough the embodiments are not limited thereto. The width W1 of thesurface irregularities SR_1 may be within a range similar to thewavelength band of light emitted from the light emitting element 30.When the light emitted from the light emitting element 30 has a firstwavelength band, the width W1 and the interval W2 of the surfaceirregularities SR_1 may be adjusted within the range of the firstwavelength band. For example, when the light emitted from the lightemitting element 30 is a blue light having a central wavelength band ofabout 450 nm to about 495 nm, the width W1 and the interval W2 of thesurface irregularities SR_1 may have a range of about 450 nm to about495 nm.

In the embodiment, the surface irregularities SR_1 formed on the topsurface 21US_3 of the first electrode 21_3 (the first surfaceirregularities) and the surface irregularities SR_1 formed on the topsurface 22US_3 of the second electrode 22_3 (the second surfaceirregularities) may be the same. However, the disclosure is not limitedthereto, and the first surface irregularities and the second surfaceirregularities may be formed differently.

FIG. 12 is an enlarged schematic cross-sectional view illustratinganother example of area A of FIG. 3.

Referring to FIG. 12, a display device according to the embodiment isdifferent from the embodiment of FIG. 11 in that it includes first andsecond contact electrodes 26_1 and 27_1 in which the patterned surfaceirregularities are formed.

The first contact electrode 26_1 and the second contact electrode 27_1may be conformally disposed on the first electrode 21_3, a secondelectrode 22_3 and the first insulating layer 51, respectively. Thesurface shape of the first contact electrode 26_1 and the second contactelectrode 27_1 may have a shape similar to the surface shape of thelayer disposed below. For example, when the surface of the layerdisposed below the first contact electrode 26_1 and the second contactelectrode 27_1 has a textured surface, the surfaces of the first contactelectrode 26_1 and the second contact electrode 27_1 may also have atextured surface, and when the surface of the layer disposed below isflat, the surfaces of the first contact electrode 26_1 and the secondcontact electrode 27_1 may also be flat. In an embodiment, the firstcontact electrode 26_1 may include surface irregularities (third surfaceirregularities) in the region directly disposed on the top surface21US_3 of the first electrode 21_3 having the surface irregularitiesSR_1 (or first surface irregularities), and may have a flat surfaceshape in the region disposed on the first insulating layer 51 having aflat surface. Similarly, the second contact electrode 27_1 may includesurface irregularities (fourth surface irregularities) in the regiondirectly disposed on the top surface 22US_3 of the second electrode 22_3having the surface irregularities SR_1 (or second surfaceirregularities), and may have a flat surface shape in the regiondisposed on the first insulating layer 51 having a flat surface. Thesurface irregularities of first and second contact electrode 26_1 and27_1 will correspond the surface irregularities SR_1 of the first andsecond electrodes 21_3 and 22_3 in the regions where the first andsecond contact electrodes 26_1 and 27_1 contact the first and secondelectrodes 21_3 and 22_3.

Although the first and second contact electrodes 26_1 and 27_1 disposedon the first and second electrodes 21_3 and 22_3 are shown to have thesame surface roughness as the surface roughness of the first and secondelectrodes 21_3 and 22_3 in the drawings, the disclosure is not limitedthereto. As the first and second contact electrodes 26_1 and 27_1 areconformally formed on the first and second electrodes 21_3 and 22_3, theshape of the surface irregularities SR_1 of the first and secondelectrodes 21_3 and 22_3 disposed thereunder may be reflected but thesize of the surface irregularities on the first and second contactelectrodes 26_1 and 27_1 may be smaller than the size of the surfaceirregularities SR_1 formed in the first and second electrodes 21_3 and22_3. For example, the surface roughness of the third surfaceirregularities of the first contact electrode 26_1 disposed on the firstelectrode 21_3 may be smaller than the surface roughness of the firstsurface irregularities of the first electrode 21_3. Similarly, thesurface roughness of the fourth surface irregularities of the secondcontact electrode 27_1 disposed on the second electrode 22_3 may besmaller than the surface roughness of the second surface irregularitiesof the second electrode 22_3.

In the embodiment, as the top surfaces of the first and second contactelectrodes 26_1 and 27_1 also include a textured surface, the occurrenceratio of the diffuse reflection that may occur at the interface betweenthe first and second contact electrodes 26_1 and 27_1 and the fourthinsulating layer 54 may be reduced. Accordingly, an optical waveguidemay be prevented from being formed by the layers disposed on the firstand second electrodes 21_3 and 22_3, thereby improving the lightemission efficiency of the display device 10.

FIG. 13 is an enlarged schematic cross-sectional view illustrating stillanother example of area A of FIG. 3.

Referring to FIG. 13, the display device according to the embodiment isdifferent from the embodiment of FIG. 12 in that it includes first andsecond sub-banks 41_1 and 42_1 having patterned surface irregularitiesformed on their surfaces.

The first and second sub-banks 41_1 and 42_1 may have patterned surfaceirregularities on their surfaces. For example, the top surface 41US_1and the first side surface 41SS1_1 of the first sub-bank 41_1 may havepatterned surface irregularities. The top surface 42US_1 and the firstside surface 42SS1_1 of the second sub-bank 42_1 may have patternedsurface irregularities.

The first electrode 21_3 may be conformally disposed on the firstsub-bank 41_1. Accordingly, the surface shape of the first electrode21_3 may have a shape similar to the surface shape of the first sub-bank41_1. For example, when the top surface 41US_1 and the first sidesurface 41SS1_1 of the first sub-bank 41_1 have patterned surfaceirregularities, the first electrode 21_3 may be conformally stacked onthe first sub-bank 41_1, so that the top surface 21US_3 of the firstelectrode 21_3 may also have patterned surface irregularities SR_1.

Similarly, the second electrode 22_3 may be disposed conformally on thesecond sub-bank 42_1. Accordingly, the surface shape of the secondelectrode 22_3 may have a shape similar to the surface shape of thesecond sub-bank 42_1. For example, when the top surface 42US_1 and thefirst side surface 42SS1_1 of the second sub-bank 42_1 have patternedsurface irregularities, the second electrode 22_3 may be conformallystacked on the second sub-bank 42_1, so that the top surface 22US_3 ofthe second electrode 22_3 may also have the surface irregularities SR_1.

FIG. 14 is an enlarged schematic cross-sectional view illustrating stillanother example of area A of FIG. 3.

Referring to FIG. 14, the display device 10 according to the embodimentis different from the embodiment of FIG. 3 in that the third insulatinglayer 53 is omitted.

The first contact electrode 26 and the second contact electrode 27 maybe directly disposed on the second insulating layer 52. The firstcontact electrode 26 and the second contact electrode 27 may be spacedapart from each other on the second insulating layer 52 to expose a partof the second insulating layer 52. The second insulating layer 52exposed by the first contact electrode 26 and the second contactelectrode 27 may contact the fourth insulating layer 54 in the exposedregion.

In the embodiment, even when the third insulating layer 53 is omitted inthe display device 10, the second insulating layer 52 may include anorganic insulating material to perform the function of fixing the lightemitting element 30. The first contact electrode 26 and the secondcontact electrode 27 may be patterned and formed simultaneously by asingle mask process. Accordingly, since no additional mask process isrequired to form the first contact electrode 26 and the second contactelectrode 27, the process efficiency may be improved. The embodiment isthe same as the embodiment of FIG. 3 except that the third insulatinglayer 53 is omitted, and thus the description of the same componentswill not be repeated.

Embodiments have been disclosed herein, and although terms are employed,they are used and are to be interpreted in a generic and descriptivesense only and not for purpose of limitation. In some instances, aswould be apparent by one of ordinary skill in the art, features,characteristics, and/or elements described in connection with anembodiment may be used singly or in combination with features,characteristics, and/or elements described in connection with otherembodiments unless otherwise specifically indicated. Accordingly, itwill be understood by those of ordinary skill in the art that variouschanges in form and details may be made without departing from thespirit and scope of the disclosure as set forth in the following claims.

What is claimed is:
 1. A display device comprising: a first reflectiveelectrode disposed on a surface of a substrate, and including firstsurface irregularities disposed on a top surface of the first reflectiveelectrode; a second reflective electrode spaced apart from the firstreflective electrode, disposed on the surface of the substrate, andincluding second surface irregularities disposed on a top surface of thesecond reflective electrode; and a light emitting element disposedbetween the first reflective electrode and the second reflectiveelectrode.
 2. The display device of claim 1, wherein each of the firstreflective electrode and second reflective electrode comprises silver,aluminum, gold, platinum, palladium, indium, nickel, chrome, or an alloythereof.
 3. The display device of claim 1, further comprising: a firstinsulating layer disposed on the first reflective electrode and thesecond reflective electrode, wherein the first insulating layer exposesat least a part of the first reflective electrode and at least a part ofthe second reflective electrode, and the light emitting element isdisposed on the first insulating layer.
 4. The display device of claim3, further comprising: a first contact electrode disposed on the firstreflective electrode, the first contact electrode electricallycontacting the first reflective electrode exposed by the firstinsulating layer and electrically contacting a first end of the lightemitting element; and a second contact electrode disposed on the secondreflective electrode, the second contract electrode electricallycontacting the second reflective electrode exposed by the firstinsulating layer and electrically contacting a second end of the lightemitting element.
 5. The display device of claim 4, further comprising:a second insulating layer disposed on the first contact electrode andthe second contact electrode, and covering the first contact electrodeand the second contact electrode, wherein a refractive index of thesecond insulating layer is different from a refractive index of thefirst contact electrode and different from a refractive index of thesecond contact electrode.
 6. The display device of claim 5, wherein therefractive index of the second insulating layer is smaller than therefractive index of the first contact electrode and smaller than therefractive index of the second contact electrode.
 7. The display deviceof claim 5, further comprising: a filler disposed on the first andsecond contact electrodes, wherein a refractive index of the filler issmaller than the refractive index of the first contact electrode andsmaller than the refractive index of the second contact electrode. 8.The display device of claim 4, wherein the first contact electrodeelectrically connects the light emitting element and the firstreflective electrode that are spaced apart from each other, and thesecond contact electrode electrically connects the light emittingelement and the second reflective electrode that are spaced apart fromeach other.
 9. The display device of claim 4, wherein the first contactelectrode includes third surface irregularities that correspond to thefirst surface irregularities of the first reflective electrode and aredisposed in a region where the first contact electrode contacts thefirst reflective electrode.
 10. The display device of claim 1, whereinthe first surface irregularities and the second surface irregularitieshave a same surface roughness.
 11. The display device of claim 1,wherein the first surface irregularities and the second surfaceirregularities each have a random shape.
 12. The display device of claim1, wherein the first surface irregularities and the second surfaceirregularities are patterned to have a constant size.
 13. The displaydevice of claim 12, wherein a size of each of the first surfaceirregularities and the second surface irregularities is within a rangeof a wavelength band of light emitted from the light emitting element.14. The display device of claim 1, further comprising: a first sub-bankdisposed on the surface of the substrate, and including a side surfacefacing a first end of the light emitting element, wherein the firstreflective electrode is disposed on the first sub-bank, and the firstsurface irregularities are disposed in a region overlapping at least theside surface of the first sub-bank.
 15. The display device of claim 14,further comprising: a second sub-bank spaced apart from the firstsub-bank, disposed on the surface of the substrate, and including a sidesurface facing a second end of the light emitting element, wherein thesecond reflective electrode is disposed on the second sub-bank, andincluding the second surface irregularities disposed in a regionoverlapping at least the side surface of the second sub-bank.
 16. Adisplay device comprising: a first electrode disposed on a substrate,and including surface irregularities disposed on a top surface of thefirst electrode; a second electrode spaced apart from the firstelectrode, disposed on the substrate, and including surfaceirregularities disposed on a top surface of the second electrode; alight emitting element disposed between the first electrode and thesecond electrode; a first contact electrode disposed on the firstelectrode, the first contact electrode electrically connecting the firstelectrode to a first end of the light emitting element; a second contactelectrode disposed on the second electrode, the second contact electrodeelectrically connecting the second electrode to a second end of thelight emitting element; and an insulating layer disposed on the firstcontact electrode and the second contact electrode, and covering thefirst contact electrode and the second contact electrode, wherein arefractive index of the insulating layer is different from a refractiveindex of the first contact electrode and different from a refractiveindex of the second contact electrode.
 17. The display device of claim16, wherein the refractive index of the insulating layer is smaller thanthe refractive index of the first contact electrode and smaller than therefractive index of the second contact electrode.
 18. The display deviceof claim 17, wherein each of the first electrode and the secondelectrode comprises silver, aluminum, gold, platinum, palladium, indium,nickel, chrome, or an alloy thereof.
 19. The display device of claim 17,wherein the surface irregularities of the first electrode and thesurface irregularities of the second electrode are patterned to have aconstant size.
 20. The display device of claim 19, wherein a size ofeach of the surface irregularities of the first electrode and thesurface irregularities of the second electrode is within in a range of awavelength band of light emitted from the light emitting element.